Workpiece Geometry Research Articles

Simulation based iterative post-optimization of paths of robot guided thermal spraying

Abstract Robot-based thermal spraying is a production process in which an industrial robot guides a spray gun along a path in order to spray molten material onto a workpiece surface to form a coating of desired thickness. This paper is concerned with optimizing a given path of this sort by post-processing. Reasons for doing so are to reduce the thickness error caused by a not sufficiently precise design of the given path, to adapt the path to a changed spray gun or spray technology, to adapt the path to slight incremental changes of the workpiece geometry, or to smooth the path in order to improve its execution by the robot. An approach to post-optimization using the nonlinear conjugate gradient method is presented which employs a high-quality GPGPU-based simulation of the spray process for the evaluation of the coating thickness error and additionally taking care of the kinematic path quality. The number of computationally time-consuming calls of the simulation is kept low by analytically calculating estimates of gradients from a simplified material deposition model. A rigorous experimental evaluation on case studies of the mentioned applications shows that the method efficiently delivers improved paths which reduce the coating error on real free form surfaces considerably, i.e. the squared coating error is below 3.5% of the original value in every case study.

Kinematics and trajectory of both-sides cylindrical lapping process in planetary motion type

The both-sides lapping process in planetary motion type is proposed in this paper to lap and polish the cylindrical surface of bearing roller. The rolling speed of roller is the key kinematical parameter that affects the generation of cylindrical surface of roller. Through analysis of friction forces and pure rolling motion, it was discovered that the rolling speed of roller only depends on the rotation speed of lower plate rather than upper plate. Based on the above result, the geometry and kinematics of workpiece in this method is described, and the functions are proved valid by an experiment in which the rolling speed of roller is observed in video. By theoretical tests under different speed conditions, it is indicated that the roller's rolling speed varies with respect to time along a nonstandard cosine curve with an offset, its amplitude depends on the speeds of lower plate rotation and carrier circulation, and its offset depends on the speeds of lower plate rotation and carrier rotation. Based on geometry and kinematics, the trajectories on the cylindrical surface of roller and on the flat surface of plate are both described and simulated. The standard deviation and the range of path curve length distribution density are applied to numerically evaluate and analyze the trajectory distribution. The effect of speed parameters on the trajectory distribution, and the generation of trajectory with respect to time are investigated.

Multi-criteria decision making techniques for compliant polishing tool selection

Precision devices require surface finish of a few nanometers. The choice of compliant coated abrasive tools used in manufacturing such devices is discussed including a method for selecting a suitable one for a given component using decision-making techniques. Multiple conflicting criteria such as surface roughness and the polishing time influence the selection of appropriate compliant polishing tool. Hence, multi-criteria decision making methods (MCDMs) are implemented to rank the suitability of different polishing processes for a given workpiece geometry. New criteria such as compliance and surface integrity are introduced for such selection. In order to differentiate the level of complexity involved in these MCDMs, a traditional analytical hierarchy process (AHP) and a Fuzzy VIsekriterijumsko KOmpromisno Resenje (multi-criteria optimization and compromise solution, VIKOR) method are chosen. This study illustrates the capability of these two MCDMs as a polishing process selection tool using the linguistic information through a case study. From the decision makers’ inputs, rankings of polishing tools were obtained and compared using these two methods. New factors such as compliance are seen to affect the choice significantly. The approach discussed in this work could be used for developing an intelligent decision-making system for choosing polishing tools with respect to the given conditions.

Thermal Analysis of Creep Feed Grinding

Creep feed grinding is an abrasive finishing process characterized by low feed speeds (0.05-0.5 m/min) and very high depths of cut (0.1-30mm). Thanks to the extraordinary material removal rate provided together with a high shape accuracy obtained over complex profiles, this process has become the main competitor of milling. However, creep feed grinding has also some limitations that should be overcome. The major limitation is the thermal damage on the machined part and the rapid wheel wear. Since heat distribution depends strongly on the workpiece geometry, a 3D FEM thermal model has been programmed for the generation of a square in order to study the effect of the side wall height on the heat distribution on both, the wall and the ground part. Thermal model has been validated by means of experimental tests being the heat ratio to the workpiece the adjusting parameter. General results show that the higher the side wall, the higher the temperatures. Friction between the wheel and the side wall contributes to higher power consumption.

A Meta-model Framework forGrinding Simulation

When considering the mechanics of grinding, several physical phenomena have to be modeled, each one having effect on the resulting grinding forces, wheel and workpiece geometry. Depending on the analyzed problem, some dependencies can be neglected to privilege some aspects instead of others. Nevertheless, all models essentially start considering wheel-workpiece engagement and the corresponding material removal (both wheel and workpiece side), deriving the forces by means of energy balances and/or shear mechanics. The meta-model proposed in this paper represents a general framework conceived for providing a time-domain simulation engine based on a dexel representation of wheel and workpiece, capable to “host” all the semi-empirical models existing in literature, where the overall grinding force is the result of the integration of the force contributions associated to the local removal along wheel-workpiece engagement arc. A cascade approach is adopted to solve for forces and displacements the DAEs set describing the dynamic interactions between wheel and workpiece, whereas all the algebraic relationships pertaining to the various specific models are solved in a pre-processing phase, yielding a set of response surfaces that are queried during time integration. Finally, the meta-model framework is instantiated for a model of traverse roll grinding with force-dependent wheel wear.

Prediction of Cutting Force in 3-Axis CNC Milling Machines Based on Voxelization Framework for Digital Manufacturing

A new digital-based model is presented for the prediction cutting forces in 3-axis CNC milling of surfaces. The model uses an algorithm to detect the work-piece/cutter intersection domain automatically for given cutter location (CL), cutter and work-piece geometries. The algorithm uses a voxelization framework to voxelize the cutter helix as well as the work-piece and based on voxel intersections between them can detect the tool engagement. Furthermore, an analytical approach is used to calculate the cutting forces based on the discretized model. The results of model validation experiments on machining PMMA and Aluminum 6061 are also reported. Comparisons of the predicted and measured forces show that this digital approach can be used to accurately predict forces during machining.

Traceability of In-process Measurement of Workpiece Geometry

In-process metrology is applied in industrial processes with the aim of obtaining and analysing quality data directly in the manufacturing process. An effective approach for improving the manufacturing processes is the incorporation of traceable dimensional metrology directly on machine tools. European project EMRP IND62 TIM that was agreed between EC and European metrology association Euramet is aimed to introduce a traceability chain into in-process geometrical measurements. One of the tasks of the project is to develop highly accurate robust temperature invariant measurement standards that can be used in the harsh environment of the production floor for verification and mapping of the measurement errors of machine tools. Laboratory for Production measurement (LTM) at the University of Maribor - Faculty of Mechanical Engineering is taking part in the consortium of this joint research project. The main task of LTM is to develop, manufacture and calibrate at least 1D measurement standard with length up to 2 m and with thermal expansion coefficient close to 0. The task will be performed in co-operation with EMO Orodjarna, Gorenje Orodjarana and Veplas. The design is based on composite body and ceramic probing balls. Original approach of compensating thermal expansion was introduced in order to enable use of the standard in harsh environmental conditions. The article presents basic principles of in-process measurement traceability as well as the physical standard under development and application possibilities of this standard.

Study of the Milling Process for Thin Components Using a Flexible Setup Configuration

In the aerospace industry, numerous large parts with complex curvatures and several thin wall/web pockets are required to ensure stiffness and low weight for aircraft structures. Costly processes and dedicated setups are usually required to machine such thin plate components. Therefore, investigating new machining methods involving flexible setups for such parts is an interesting avenue for cost savings, but a big challenge as well, due to a lack of support and part flexibility. In fact, a flexible setup is a tooling system with several adjustable positioning supports, which can easily adapt to different workpiece geometries. In this paper, an experimental investigation of the machining of pockets for thin components using flexible setup is presented. A design of experiments is proposed to verify the ability of pocket machining for thin plates of aluminum 2024-T3 in terms of quality. During the machining tests, the cutting forces were measured using a Kistler dynamometer table, while the displacement of the plates, for the flexible setup configuration, was measured using a Keyence displacement sensor. The force and displacement signals were analyzed and a fine correlation proposed between them and the resulting quality of the part, expressed in terms of profile and size errors.

A two‐scale simulation method accounting for thermal effects during turning

AbstractDuring chip formation in turning processes, mechanical work is dissipated into thermal energy by plastic deformations and frictional processes. In case of dry cutting, the generated heat is in part removed with the chips while the rest flows into the tool and the workpiece. Within the latter, the temperature increases due to this heat flow, which in turn causes thermal expansions that increase the cutting depth and thus induce deviations from the nominal workpiece geometry. These effects are treated separately by a local model for the chip formation and a global model for the whole workpiece in order to determine the temperature distribution inside the workpiece and the dependent thermal expansion. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Measurement of Twist Springback on AA6061-T6 Aluminum Alloy Strip - A Preliminary Result

Twist forming is one of a critical process in a sheet metal forming process that has a complex profile. There are a few parameters that need to be taken into consideration, such as twist angle, workpiece geometries including length, width and thickness and material properties of the workpiece material. In this study, the preliminary result of the twist forming behavior of an aluminum alloy strip with uniform section will be studied. The experiment is conducted using torsion test machine. At this stage, the torque pattern was studied and compared with the published work to validate the experiment test rig. The result showed an agreement with the published work.

Effect of tool nose profile tolerance on surface roughness in finish turning

The effect of the tool nose profile deviations in cutting tool inserts on the surface roughness of the work piece produced based on the actual tool nose profile geometry is studied. The nose profile was detected from the tool nose image captured using the 3-D metrology system. A edge detection approach combining moment invariance operator with Sobel 2-D filter operator is proposed. A work piece surface profile is then generated by considering tool nose profile deviation, feed rate, nose radius and wedge angle to study the effect of the work piece geometry deviation on the roughness values. Based on the experimental results, the maximum differences from ideal and experimental results are 19.8% for R t, 19.9% for R a and 16.1% for R q respectively.

Modelling of Tool Engagement and FEM-Simulation of Chip Formation for Drilling Processes

Drilling is the most used machining operation in modern manufacturing. Consequently, a high efficiency is desired which can achieved by proper tool geometries and process conditions. The claim for a high degree of process understanding is met by the attempt to visualize the chip formation on a micro scale, e.g. by the use of the finite element method. While two-dimensional FE-simulations of cutting processes are established 3D is the next step to take for further analysis of the drilling processes. Nevertheless, this puts high challenges to the simulative approach in order to achieve valid results. This paper deals with the modelling and the simulation of drilling operations with respect to tool and workpiece geometry. In order to create an acceptable starting condition it is useful to consider the engagement situation of the tool and the workpiece as an ideal state with a defined uncut chip thickness in front of the cutting edge. This provides shorter calculation times due to earlier steady-state chip formation compared to simulations with workpieces which are modeled with uniform surfaces like planes or cones in the initial state. Therefore, the engagement situation is created by the utilization of a geometric-kinematical modelling technique in which an array of rays and their intersections with a triangular mesh constitute a discrete description of a surface. The obtained set of points is further used for triangulation to generate the workpiece geometry mesh. Finally, finite element simulations of the drilling processes are carried out and are analyzed with respect to drilling torque and feed force.

Strain Analysis of Parts Produced by Multi-Pass Conventional Metal Spinning

Sheet metal spinning is one of the forming processes based on gradual shaping of metal blank into an axisymetric part by a roller according to a mandrel. Very significant feature of spinning is ability to produce components with high mechanical properties and high quality of surface layers. The paper brings the results of major true strains analysis of mild steel parts produced by CNC multi-pass conventional metal spinning. The influence of the spindle speed, feed rate, workpiece geometry and planar anisotropy of the blank on the strain distribution of formed part is studied by method of grain size measurement. The design of experiment using the Taguchi approach and analysis of variance (ANOVA) is applied to find optimal process parameters.

Geometrical Phenomena in Tube Bending with Local Induction Heating

A theoretical and experimental analysis of heat induction bending for tubes used in the power industry is performed. First, the design of the heat induction bending process for tubes is described and industrial application areas for this technology are presented. Next, the main methods for tube bending with local induction heating are discussed and the effect of the technology on geometrical parameters of bends formed is presented. Then, the heat induction bending process for tubes is modeled using numerical techniques (FEM). The simulations are performed in a three-dimensional strain state, where thermal phenomena are taken into account, using the commercial software package Simufact Forming v. 11.0. In the simulations, the changes in workpiece geometry in the region of the bend being made (cross section ovalization, darkening and thickening of walls, neutral axis position) are examined. Also, potential phenomena that could limit the stability of the bending process and cause shape defects are predicted. The results of the numerical modeling are then compared to those obtained under industrial conditions.

Mathematical modeling and application of removal functions during deterministic ion beam figuring of optical surfaces. Part 1: Mathematical modeling.

Ion beam figuring (IBF) is established for the final precision figuring of high-performance optical components, where the figuring accuracy is guaranteed by the stability of the removal function and the solution accuracy of the dwell time. In this deterministic method, the figuring process can be represented by a two-dimensional (2D) convolution operation of a constant removal function and the dwell time. However, we have found that the current 2D convolution operation cannot factually describe the IBF process of curved surfaces, which neglects the influences of the projection distortion and the workpiece geometry on the removal function. Consequently, the current 2D convolution algorithm would influence the solution accuracy for the dwell time and reduce the convergence of the figuring process. In this part, based on the material removal characteristics of IBF, a mathematical model of the removal function is developed theoretically and verified experimentally. Research results show that the removal function during IBF of a curved surface is actually a dynamic function in the 2D convolution algorithm. The mathematical modeling of the dynamic removal function provides theoretical foundations for our proposed new algorithm in the next part, and final verification experiments indicate that this algorithm can effectively improve the accuracy of the dwell time solution for the IBF of curved surfaces.

Mathematical modeling and application of removal functions during deterministic ion beam figuring of optical surfaces. Part 2: application.

Ion beam figuring (IBF) is established for the final precision figuring of optical components. In this deterministic method, the figuring process is represented by a two-dimensional (2D) convolution operation of a constant removal function and the dwell time, where the figuring precision is guaranteed by the stability of the removal function as well as the solution accuracy of the dwell time. However, the current 2D convolution equation cannot factually reflect the IBF process of curved surfaces, which neglects the influence of the projection distortion and the workpiece geometry. Consequently, the current convolution algorithm for the IBF process would influence the solution accuracy for the dwell time and reduce the convergence of the figuring process. In this part, we propose an improved algorithm based on the mathematical modeling of the dynamic removal function in Part A, which provides a more accurate dwell time for IBF of a curved surface. Additionally, simulation analysis and figuring experiments are carried out to verify the feasibility of our proposed algorithm. The final experimental results indicate that the figuring precision and efficiency can be simultaneously improved by this method.

A coupled electric–magnetic numerical procedure for determining the electromagnetic force from the interaction of thin metal sheets and spiral coils in the electromagnetic forming process

In this paper, a numerical procedure is proposed that is both coupled electromagnetic and uncoupled magnetic-mechanical, and enables the calculation of electromagnetic force in thin circular flat plates by using a spiral coil as an actuator. Its inductances, which link the electric and magnetic phenomena, can be calculated by treating the problem as an electric circuit. The influence of system parameters, such as pulse energy, workpiece and coil geometry and material properties, are considered in the calculation of electromagnetic force. The calculation routine models the problem as a system of ordinary differential equations to obtain the discharge (actuator coil) and induced (workpiece) currents. Free bulging experiments with discharge current acquisition were performed to demonstrate satisfactory correlation with the calculation method, which provides valuable feedback for system design.

Research on Simulation of Virtual NC Lathe Machining Process

Virtual NC lathe machining simulation system is carried out with Visual C++ and Open Inventor software. The system possesses visible UI, interactive inputting workpiece and machining parameters, the integration of geometric simulation and physical simulation, all the simulation functions including real-time display machining process, tool moving, workpiece geometry shape change, the generation and movement of iron simulation, workpiece pressure shape change could be realized. Tool temperature analysis and stress & strain analysis are simulated in the cutting process by FEM. The simulation results show the high efficiency of the simulation algorithm, reasonable simulation results, lifelike. The practice and training could be replaced by the virtual one. The system is applied to verification of NC code, quality evaluation of machine operators, operators, CNC programming staff training and other functions.

Prediction of Machining Fixture Layout through FEM and ANN and Comparison of Optimal Fixture Layouts of GA and ACA

In machine manufacturing, workholding plays a vital role in immobilizing the workpiece to provide maximum accuracy. The workpiece should be securely located and held against the cutting tool to reduce workpiece deformation thereby reducing dimensional and form errors. Fixtures are workholding devices used in machining and assembly for holding, supporting and locating a workpiece in a given orientation. Fixturing elements such as locators and clamps are used to deprive the workpiece of all degrees of freedom so that it is constrained at all times to prevent any movement. The optimal positioning of locators and clamps highly influences the workpiece deformation and thereby the machining errors. A two-dimensional workpiece geometry involving a slot milling operation has been considered for the research work for which the workpiece deformation for different fixture layouts is determined using finite element method (FEM). The different layouts and the corresponding workpiece deformations from the simulation results are made available as the database for artificial neural network (ANN) to develop a numerical model that recognizes a pattern between the position of fixturing elements and the workpiece deformations. Using the recognized pattern from ANN, genetic algorithm (GA) based continuous optimization method and ant colony algorithm (ACA) based continuous optimization method have been used to determine the optimal position of locators and clamps to minimize the workpiece deformation and thereby the dimensional errors

On a generalized approach to manufacturing energy efficiency

Energy efficiency has become a very significant factor, requiring its inclusion in the manufacturing decision-making attributes. This paper proposes a generalized approach to manufacturing energy efficiency. The basic element of the approach is the division of energy efficiency definition and study into four manufacturing levels, namely process, machine, production line, and factory. Process-level definitions are provided for the majority of manufacturing processes. A machine-level study indicates and solves difficulties, generated by the workpiece geometry, and points out the interaction with the process level through factors, such as the process time. Moreover, machine tool peripherals are responsible for a significant portion of the consumed energy, and classification based on the dependence of their consumption on process variables is required. Studies made on the production line and factory levels show that energy efficiency, at these levels, is heavily dependent on production planning and scheduling and can be improved through the appropriate utilization of machines, with the inclusion of shutdown and eco-modes. Finally, a case study is presented, showing that many of the difficulties towards the optimization of energy efficiency can be dealt with successfully, using the proposed generalized approach.